Leadless pacemaker system

ABSTRACT

A device includes a signal generator module, a processing module, and a housing. The signal generator module is configured to deliver pacing pulses to an atrium. The processing module is configured to detect a ventricular activation event and determine a length of an interval between the ventricular activation event and a previous atrial event that preceded the ventricular activation event. The processing module is further configured to schedule a time at which to deliver a pacing pulse to the atrium based on the length of the interval and control the signal generator module to deliver the pacing pulse at the scheduled time. The housing is configured for implantation within the atrium. The housing encloses the stimulation generator and the processing module.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/665,492, filed on Oct. 31, 2012, now issued as U.S. Pat. No.8,923,963.

TECHNICAL FIELD

The disclosure relates to cardiac pacing, and more particularly, totechniques for cardiac pacing using a leadless pacemaker device.

BACKGROUND

An implantable pacemaker may deliver pacing pulses to a patient's heartand monitor conditions of the patient's heart. The implantable pacemakermay comprise a pulse generator and one or more electrical leads. Thepulse generator may be implanted in a small pocket in the patient'schest in some examples. The electrical leads may be coupled to the pulsegenerator, which may contain circuitry that generates pacing pulsesand/or senses cardiac electrical activity. The electrical leads mayextend from the pulse generator to a target site (e.g., an atrium and/ora ventricle) where electrodes at the distal ends of the electrical leadsconnect to the target site. The pulse generator may provide electricalstimulation to the target site and/or monitor cardiac electricalactivity at the target site via the electrodes.

In some examples, a leadless pacemaker may be used to sense electricalactivity and/or deliver therapeutic signals to the heart. The leadlesspacemaker may include one or more electrodes on its outer housing todeliver therapeutic electrical signals and/or sense intrinsicdepolarizations of the heart. The leadless pacemaker may be positionedwithin or outside of the heart and, in some examples, may be anchored toa wall of the heart via a fixation mechanism.

SUMMARY

A leadless atrial pacing device (hereinafter “atrial device”) of thepresent disclosure is configured for implantation within the atrium of apatient's heart. The atrial device may pace the atrium, sense intrinsicatrial electrical activity, and detect ventricular activation. Theatrial device may be configured to detect ventricular activation bydetecting ventricular electrical activity and/or mechanical contractionof the ventricles. The atrial device may control the timing of pacingpulses delivered to the atrium based on when ventricular activation isdetected.

The atrial device may operate as the sole pacing device implanted in theheart in some examples. In other examples, the atrial device may operatealong with a leadless ventricular pacing device (hereinafter“ventricular device”) that is configured for implantation within aventricle of the patient's heart. The ventricular device may beconfigured to sense intrinsic ventricular depolarizations and pace theventricle. In some examples, the ventricular device may be programmedsuch that the ventricular device paces at a backup pacing rate (e.g.,less than the atrial pacing rate) for situations in which atrialdepolarization does not precipitate a ventricular depolarization, e.g.,during AV block.

The combination of the atrial and ventricular devices may be referred toherein as a leadless pacing system. The atrial device of the presentdisclosure may operate reliably without modification (e.g.,reprogramming) when the ventricular device has been added to thepatient's heart to form a leadless pacing system. The atrial device mayoperate reliably even when the ventricular device is added because theatrial device controls atrial pacing timing based on sensed ventricularactivation, independent on the origin of the sensed ventricularactivation. Accordingly, the atrial device of the present disclosure mayfunction in a variety of different scenarios without modification, e.g.,as a stand-alone pacing device or implanted along with another pacingdevice.

The leadless pacing system may coordinate pacing of the heart based onsensed cardiac electrical and/or mechanical activity withoutestablishment of a communication link between the atrial device and theventricular device. In this manner, the atrial device and theventricular device may operate independently from one another in thesense that operation of the atrial and ventricular devices may depend onsensed cardiac activity (electrical or mechanical) and may not need torely on wired or wireless communication, unlike typical pacemakersincluding pulse generators and electrical leads. Since the atrial deviceand the ventricular device do not rely on communication to coordinatepacing of the heart, the atrial and ventricular devices may save powerthat otherwise would be used to coordinate operation of the devices viacommunication.

In some examples, a device according to the present disclosure comprisesa signal generator module, a processing module, and a housing. Thesignal generator module is configured to deliver pacing pulses to anatrium. The processing module is configured to detect a ventricularactivation event and determine a length of an interval between theventricular activation event and a previous atrial event that preceded(e.g., precipitated) the ventricular activation event. The processingmodule is further configured to schedule a time at which to deliver apacing pulse to the atrium based on the length of the interval andcontrol the signal generator module to deliver the pacing pulse at thescheduled time. The housing is configured for implantation within theatrium. The housing encloses the stimulation generator and theprocessing module.

In some examples, a method according to the present disclosure comprisesdetecting a ventricular activation event using an atrial pacing deviceconfigured for implantation within an atrium and determining a length ofan interval between the ventricular activation event and a previousatrial event that preceded the ventricular activation event. The methodfurther comprises scheduling a time at which to deliver a pacing pulseto the atrium based on the length of the interval and delivering thepacing pulse at the scheduled time.

In some examples, a device according to the present disclosure comprisesa signal generator module, a processing module, and a housing. Thesignal generator module is configured to deliver pacing pulses to anatrium. The processing module is configured to detect a firstventricular activation event, detect a second ventricular activationevent subsequent to the first ventricular activation event, anddetermine a length of an interval between the first and secondventricular activation events. The processing module is furtherconfigured to schedule a time at which to deliver a pacing pulse to theatrium based on the length of the interval and control the signalgenerator module to deliver the pacing pulse at the scheduled time. Thehousing is configured for implantation within the atrium. The housingencloses the stimulation generator and the processing module.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example leadless pacemaker device.

FIG. 2 is a functional block diagram of the example leadless pacemakerdevice.

FIG. 3 shows an example leadless pacemaker device implanted in a patientthat may be used to diagnose conditions of and provide therapy to aheart of the patient.

FIG. 4 is an example atrial pacing timing diagram during normalatrioventricular (AV) conduction that includes ventricular activation(V_(ACT)) markers.

FIG. 5 is a flowchart of a method for controlling atrial pacing timingbased on detection of ventricular activation.

FIG. 6 is an example atrial pacing timing diagram during normal AVconduction that includes detected far-field R-waves.

FIGS. 7A-7B are example atrial pacing timing diagrams including shortintervals between atrial events and subsequently detected far-fieldR-waves.

FIGS. 8A-8B are example atrial pacing timing diagrams including longintervals between atrial events and subsequently detected far-fieldR-waves.

FIG. 9 is an example atrial pacing timing diagram including an intervalin which a far-field R-wave is undetected.

FIG. 10 is an example atrial pacing timing diagram including an intervalin which multiple far-field R-waves are detected between atrial events.

FIG. 11 shows an example leadless pacing system including an atrialpacemaker device and a ventricular pacemaker device.

FIG. 12 is a functional block diagram of the example ventricular device.

DETAILED DESCRIPTION

An implantable atrial pacing device (hereinafter “atrial device”) of thepresent disclosure is configured for implantation within the atrium of apatient's heart. The atrial device may pace the atrium, sense intrinsicatrial electrical activity, and detect ventricular activation. Theatrial device may control the timing of pacing pulses delivered to theatrium based on the detected ventricular activity.

The atrial device may include a hermetically sealed housing having asize and form factor that allows the atrial device to be implantedwithin the atrium. In some examples, the housing may have a cylindrical(e.g., pill-shaped) form factor. The housing may include fixation tinesthat connect the housing to the cardiac tissue within the atrium. Thefixation tines may anchor the atrial device to the atrial cardiac tissuesuch that the atrial device moves along with the atrial cardiac tissueduring cardiac contractions.

The housing of the atrial device may house components for sensingcardiac electrical activity such as intrinsic atrial depolarizations andventricular depolarizations, e.g., far-field R-waves (FFRWs). The atrialdevice may also house components for delivering electrical stimulationtherapy, such as pacing pulses. In some examples, the atrial device mayalso house components for sensing physiological parameters, such asacceleration, pressure, sound, and/or impedance.

The atrial device may include a plurality of electrodes used for sensingcardiac electrical activity and delivering electrical stimulationtherapy (e.g., pacing pulses). For example, the atrial device mayinclude a tip electrode and a ring electrode. The tip electrode may belocated on the housing such that the tip electrode contacts the cardiactissue when the atrial device is anchored to the cardiac tissue by thefixation tines. The ring electrode may also be located on the housing.For example, the ring electrode may be disposed around the circumferenceof the housing.

The atrial device may be configured to detect ventricular activationevents. Ventricular activation may generally refer to electricaldepolarization of the ventricular cardiac tissue and the subsequentmechanical contraction of the ventricular cardiac tissue. The atrialdevice may be configured to detect ventricular activation based on thedetection of ventricular electrical activity and/or based on thedetection of mechanical contraction of the ventricles. As used herein,detection of ventricular activation may generally refer to the detectionof ventricular electrical activity (e.g., FFRWs) and/or the detection ofmechanical contraction of the ventricles (e.g., based on heart sounds).In some examples, the atrial device may detect ventricular activation bydetecting FFRWs. In some examples, the atrial device may detectventricular activation by detecting S1 heart sounds. Although the atrialdevice may detect ventricular activation based on FFRWs and/or heartsounds, it is contemplated that the atrial device may detect ventricularactivation using other sensors and techniques.

In some examples, the atrial device may detect FFRWs in the atrium whichare indicative of a ventricular depolarization. For example, the atrialdevice may detect FFRWs and determine when ventricular depolarizationhas occurred based on the detection of FFRWs. Although the atrial deviceis described herein as detecting ventricular depolarization based on thedetection of FFRWs, it is contemplated that the atrial device may detectventricular depolarization based on detected ventricular electricalactivity other than FFRWs.

Additionally, or alternatively, the atrial device may be configured todetect mechanical contraction of the ventricles. For example, the atrialdevice may detect physiological parameters other than cardiac electricalactivity, such as acceleration and/or pressure. In some examples, theatrial device may include one or more sensors that measure accelerationand/or pressure in the atrium. In these examples, the atrial device maydetect mechanical contraction of the ventricles based on signalsgenerated by the one or more sensors. For example, the atrial device maydetect S1 heart sounds indicative of closure of the atrioventricularvalves at the beginning of ventricular contraction and then determinethat ventricular contraction has occurred based on the detection of S1heart sounds. Additionally, or alternatively, the atrial device maydetect S2 heart sounds in some examples, and then determine thatventricular contraction has occurred based on the detection of S2 heartsounds.

The atrial device may control atrial pacing timing based on whenventricular activation is detected during a cardiac cycle. In someexamples, the atrial device may determine when to pace the atrium basedon when FFRWs are detected during the cardiac cycle. Additionally, oralternatively, the atrial device may determine when to pace the atriumbased on when S1 heart sounds are detected during the cardiac cycle. Acardiac cycle may refer to cardiac electrical activity that occurs fromthe beginning of one heartbeat to the beginning of the next heartbeat,as sensed by electrodes and/or sensors of the atrial device. Componentsof the atrial device that sense cardiac electrical activity, sensecontraction of the ventricles, and control the delivery of electricalstimulation to the atrium are described hereinafter.

The atrial device may include an electrical sensing module (i.e.,sensing module) that is configured to monitor cardiac electricalactivity in the atrium. The sensing module may include electroniccomponents that acquire cardiac electrical signals via the electrodes ofthe atrial device (e.g., the tip and ring electrodes). In some examples,the sensing module may implement signal conditioning on the acquiredelectrical signals. For example, the sensing module may filter, amplify,and digitize the acquired electrical signals. The electrical activitymonitored by the sensing module may include a variety of differentelectrical signal components. The electrical activity may includeintrinsic cardiac electrical activity, e.g., intrinsic atrial activityand/or intrinsic ventricular electrical activity, or other electricalsignals.

The atrial device may include one or more sensors, such as anaccelerometer and/or a pressure sensor. An accelerometer included in theatrial device may generate signals that indicate the acceleration of theatrial device. A pressure sensor included in the atrial device maygenerate signals that indicate pressure within the atrium. When theatrial device includes a pressure sensor or an accelerometer, the atrialdevice may detect ventricular activation based on signals generated bythe sensors. For example, as described above, the atrial device maydetect contraction of the ventricles based on sensor signals indicativeof ventricular contraction, such as S1 heart sounds.

The atrial device may include a stimulation generator module (i.e.,“stimulation generator”) that is configured to deliver electricalstimulation to the atrium via the electrodes (e.g., the tip and ringelectrodes). For example, the atrial device may deliver pacing pulses tothe atrium via the electrodes. In some examples, the atrial device maydeliver electrical stimulation other than pacing pulses, such asanti-tachycardia pacing (ATP) therapy.

The atrial device may include a processing module that receives sensingdata from the sensing module. The data received from the sensing modulemay include digitized electrical activity that was received via theelectrodes of the atrial device. The processing module may detectintrinsic atrial activity based on the sensing data received from thesensing module. For example, the processing module may detect anintrinsic atrial depolarization based on the sensing data received fromthe sensing module. Detection of intrinsic atrial depolarization by theprocessing module may be referred to as an “atrial sensed event” or a“sensed atrial event” in some examples. Atrial electrical activity thatis precipitated by delivery of a pacing pulse from the stimulationgenerator may be referred to as an “atrial paced event.”

The processing module may detect ventricular activation events in avariety of different ways. In some examples, the processing module maydetect ventricular electrical activity (e.g., FFRWs). In some examples,the processing module may detect ventricular contraction based onsignals received from the one or more sensors included in the atrialdevice. For example, the processing module may detect heart sounds(e.g., the S1 heart sound) based on the signals received from the one ormore sensors and detect ventricular contractions based on the detectedheart sounds. Heart sounds may be mechanical perturbations generatedduring contractions of the heart, such as blood flow and the closing ofheart valves. The sensors (e.g., acceleration and/or pressure sensors)may generate signals in response to the mechanical perturbations. Heartsounds may be referred to as S1, S2, S3, or S4 heart sounds, forexample. The S1 heart sound may be caused by closure of theatrioventricular valves, e.g., the tricuspid and/or mitral valves at thebeginning of ventricular contraction. As such, the S1 heart sound mayindicate ventricular contraction. The processing module may also detectheart sounds S2, S3, and S4 in some examples, and determine othercardiac parameters based on the detected heart sounds.

As described above, the processing module may detect ventricularactivation based on the detection of ventricular electrical activity(e.g., FFRWs) and/or based on the detection of other ventricularcontractions (e.g., S1 heart sounds). In some examples, the processingmodule may detect ventricular activation based only on detectedventricular electrical activity. In other examples, the processingmodule may detect ventricular activation based only on the detection ofventricular contractions, e.g., based only on accelerometer data and/orpressure data. In still other examples, the processing module may detectventricular activation based on a combination of both ventricularelectrical activity and detected ventricular contractions, e.g., bothFFRWs and S1 heart sounds.

The processing module may control when the stimulation generatordelivers pacing pulses (i.e., atrial pacing timing) based on when theprocessing module detects ventricular activation during a cardiac cycle.For example, the processing module may first determine an amount of timebetween a ventricular activation event and a previous atrial event(e.g., an intrinsic or paced atrial event) that preceded the detectedventricular activation event. Then, the processing module may schedule atime at which to deliver a pacing pulse to the atrium based on thedetermined amount of time between the ventricular activation event andthe previous atrial event. The processing module may then control thesignal generator module to deliver the pacing pulse to the atrium at thescheduled time. In some examples, the processing module may beconfigured to inhibit delivery of a pacing pulse at the scheduled timeif the processing module senses an intrinsic atrial depolarizationbefore the scheduled time at which the pacing pulse was to be delivered.

The processing module may control atrial pacing timing based on thedetection of ventricular activation in a variety of different ways. Themanner in which the processing module controls atrial pacing timing maydepend on when ventricular activation occurs relative to the atrialevent that preceded (e.g., precipitated) the ventricular activation. Forexample, the manner in which the processing module controls atrialpacing timing may depend on when a FFRW is sensed relative to the atrialevent that preceded the FFRW. As another example, the manner in whichthe processing module controls atrial pacing timing may depend on whenan S1 heart sound is sensed relative to the atrial event that precededthe contraction causing the sensed S1 heart sound.

The amount of time between an atrial event (paced or sensed) and asubsequent ventricular activation event preceded by the atrial event maybe generally referred to herein as an “A-V_(ACT) interval.” Accordingly,the processing module may control atrial pacing timing based on thevalue of the A-V_(ACT) interval. An A-V_(ACT) interval is illustrated as135 in FIG. 4. In FIG. 4, the A-V_(ACT) interval has a value of T1seconds. In examples where the processing module detects FFRWs, theamount of time between the atrial event and subsequent detection of aFFRW may be referred to herein as an “A-FF interval.” In these examples,the processing module may control atrial pacing timing based on thevalue of the A-FF interval. FIGS. 6-10 illustrate various different A-FFintervals, which may depend on various different heart conditions and/orpacing programs implemented by the processing module.

As described above, the processing module may control atrial pacingtiming based on the length of the A-V_(ACT) interval. In some examples,A-V_(ACT) intervals may be approximately equal over a plurality ofcardiac cycles. In other examples, A-V_(ACT) intervals may vary over aplurality of cardiac cycles. For example, for two consecutive cardiaccycles, the A-V_(ACT) interval of the second cardiac cycle may bedifferent than the A-V_(ACT) interval of the first cardiac cycle. Theprocessing module may control atrial pacing timing during a singlecardiac cycle based on the A-V_(ACT) interval associated with thatsingle cardiac cycle in some examples. In other examples, the processingmodule may control atrial pacing timing based on a plurality ofA-V_(ACT) intervals that have occurred over a plurality of previouscardiac cycles.

The processing module may control atrial pacing timing in different waysdepending on the duration of the A-V_(ACT) interval. In general, theA-V_(ACT) interval may be characterized as having a normal duration, ashort duration, or a long duration. Operation of the atrial device inresponse to normal A-V_(ACT) intervals is illustrated in FIG. 4.Operation of the atrial device in response to normal A-FF intervals,short A-FF intervals, and long A-FF intervals is illustrated in FIGS.6-8B. Although FIGS. 6-10 illustrate atrial pacing timing based on thedetection of FFRWs, the timing diagrams of FIGS. 6-10 may be generallyapplicable to scenarios in which ventricular activation is detectedusing other techniques. For example, the timing diagrams of FIGS. 6-10may be similar to timing diagrams in cases where the processing modulecontrols atrial pacing timing based on S1 heart sounds. In one example,timing diagrams showing operation of the atrial device using S1 heartsounds instead of FFRWs may include S1 markers indicating when S1 heartsounds are detected instead of FF symbols indicating when FFRWs aredetected. Accordingly, although the timing diagrams of FIGS. 6-10,illustrating detection of FFRWs, are used to describe the operation ofthe atrial device, the atrial device of the present disclosure mayoperate in a similar manner as illustrated in FIGS. 6-10 when detectingventricular activation using other techniques, such as using S1 heartsounds.

In general, during normal AV conduction in the heart, the processingmodule may control the stimulation generator to deliver pacing pulses ata baseline atrial pacing rate (e.g., 60 bpm) such that the intervalsbetween atrial events are approximately equal over a plurality ofcardiac cycles. Normal AV conduction in the heart may refer to thescenario in which there is normal electrical continuity between theatria and ventricles. During normal AV conduction in the heart, theA-V_(ACT) interval may be characterized as having a normal duration.Normal duration for the A-V_(ACT) interval when the heart is being pacedat 60 beats per minute (bpm) may be approximately 250-350 ms. Forexample, the delay between the atrial event and ventricular activationmay be approximately 150 ms, while the delay from ventricular activationto detection of the ventricular activation, e.g., via detection of aFFRW, may be approximately 100 ms. The delay from ventricular activationto the detection of ventricular activation by the atrial device may becharacterized on a per-patient basis in some examples. Accordingly,normal, short, and long A-V_(ACT) intervals described herein may be seton a per-patient basis in some examples.

FIG. 4 illustrates atrial pacing timing based on detected ventricularactivations (e.g., FFRWs or S1 heart sounds) during normal AVconduction. In FIG. 4, the A-V_(ACT) (e.g., A-FF) interval has aconsistent value of T1, while the intervals between consecutive atrialevents (i.e., the A-A interval) consistently have a value of T3. Theprocessing module may set the pacing pulse to occur a period of timeafter detection of ventricular activation. For example, during normal AVconduction (e.g., when the A-V_(ACT) interval is approximately equal toT1), the processing module may set a pacing pulse to occur T2 secondsafter the detected ventricular activation. Similarly, when processingmodule controls atrial pacing timing based on the detection of FFRWs,the processing module may set pacing pulses to occur approximately T2seconds after a detected FFRW, as illustrated in FIG. 6.

The processing module may control the duration of time between thedetection of ventricular activation and the delivery of the next pacingpulse. For example, when the processing module detects an A-V_(ACT)interval having a duration T1 (i.e., a normal AV interval), theprocessing module may set the atrial pacing pulse to occur at a timethat is approximately T2 seconds after the detected V_(ACT). Theprocessing module may determine the value T2 based on a baseline atrialpacing interval value (e.g., T3) and the length of the A-V_(ACT)interval (e.g., T1). The baseline atrial pacing interval T3 may be aninterval stored in memory of the atrial device, which may be updatedover time in some examples. The baseline atrial pacing interval may bethe reciprocal value of the baseline atrial pacing rate (e.g., 60 bpm).During normal AV conduction where the A-V_(ACT) interval has a normalduration of T1, the processing module may schedule pacing pulses suchthat atrial events are separated by the baseline atrial pacing interval.The processing module may update the baseline pacing rate (or interval)over time based on a variety of factors, such as an activity level ofthe patient. For example, the processing module may set the baselineatrial pacing rate at approximately 60 bpm when the patient is at restand then increase the baseline atrial pacing rate to a value greaterthan 60 bpm when the processing module determines that a patient isactive (e.g., based on signals from an activity sensor).

During normal AV conduction, the processing module may determine theV_(ACT)-A interval (i.e., T2), and, therefore, when the pacing pulse isto be delivered, by subtracting the A-V_(ACT) interval (e.g., T1) fromthe baseline atrial pacing interval (e.g., T3). For example, assumingthat ventricular activation is detected T1 seconds after an atrial event(sensed or paced), the processing module may subtract the A-V_(ACT)interval of T1 from the baseline atrial pacing interval T3 to determinethe value T2. The processing module may then control the stimulationgenerator to deliver a pacing pulse that occurs T2 seconds after thedetection of ventricular activation. In this manner, during normal AVconduction over a plurality of cardiac cycles, the processing module maycontrol the stimulation generator to deliver pacing pulses such that thebaseline atrial pacing rate is maintained over the plurality of cardiaccycles.

The timing between ventricular activation and the atrial event thatpreceded the ventricular activation may deviate from the normalA-V_(ACT) interval in a variety of ways. In some examples, the A-V_(ACT)interval may be shortened (e.g., the A-FF interval is less than T1). TheA-V_(ACT) interval (e.g., A-FF interval or A-S1 interval) may beshortened in some examples due to a premature ventricular contraction(PVC). In other examples, the A-V_(ACT) interval may be lengthened(e.g., the A-FF interval is greater than T1). The A-V_(ACT) interval(e.g., A-FF interval or A-S1 interval) may be lengthened in someexamples due to AV block.

A normal A-V_(ACT) interval may be stored in memory. A normal A-V_(ACT)interval or normal A-FF interval may be referred to herein as a“baseline AV value” in some examples because the normal A-V_(ACT)interval or normal A-FF interval may be the expected value of theinterval between an atrial event and a ventricular activation duringnormal AV conduction in the heart. The normal A-V_(ACT) interval (i.e.,baseline AV value) may be associated with the baseline atrial pacinginterval in memory. For example, a normal A-V_(ACT) interval may beapproximately 250 ms when the baseline atrial pacing interval is 1000 ms(i.e., an atrial rate of 60 bpm). The baseline AV value may be updatedalong with the baseline atrial pacing interval in some examples. Ingeneral, the baseline AV value may be shortened/lengthened duringperiods of detected exercise/relaxation in examples where the atrialdevice is configured to detect the activity level of the patient, e.g.,using an activity sensor.

In some examples, the processing module may determine that the A-V_(ACT)interval is a short A-V_(ACT) interval when the A-V_(ACT) interval isshorter than the normal A-V_(ACT) interval by a threshold amount oftime. Similarly, the processing module may determine that the A-V_(ACT)interval is a long A-V_(ACT) interval when the detected A-V_(ACT)interval is longer than a normal A-V_(ACT) interval by a thresholdamount of time.

In other examples, ventricular activation may go undetected during somecardiac cycles. The A-V_(ACT) interval may go undetected when theprocessing module does not detect a FFRW, e.g., because of a weakelectrical signal or excessive noise, or because AV block has caused noV_(ACT) to occur. For example, the processing module may determine thatventricular activation is not detected during a cardiac cycle whenventricular activation has not been detected within a threshold amountof time after an atrial event. In still other examples, the processingmodule may detect multiple ventricular activations subsequent to asingle atrial event before another atrial event is detected. Multipleventricular activations may be detected after a single atrial event insome examples due to PVCs.

Operation of the atrial device during short A-V_(ACT) intervals, longA-V_(ACT) intervals, undetected ventricular activations, and multipleventricular activations is described hereinafter. Description of atrialpacing timing based on the detection of FFRWs in response to short A-FFintervals, long A-FF intervals, undetected FFRWs, and multiple FFRWs isdescribed in detail with respect to FIGS. 6-10.

In examples where the processing module detects a short A-V_(ACT)interval, the processing module may maintain the normal V_(ACT)-Ainterval timing (e.g., T2) such that the V_(ACT)-V_(ACT) interval willbe maintained during the subsequent cardiac cycle, assuming theA-V_(ACT) interval of the subsequent cycle returns to the normalduration of T1. FIG. 7A shows an example in which the processing moduledetects a shortened A-FF interval at 140 and maintains the FF-A intervalsuch that the FF-FF interval is maintained. In FIG. 7A, the A-FFinterval returns to the normal duration after the shortened A-FFinterval. Maintaining the V_(ACT)-V_(ACT) interval may promote regularV_(ACT)-V_(ACT) timing which may cause a smoothing of the ventricularrate. In examples where a ventricular pacing device (e.g., ventriculardevice 200 of FIGS. 11-12) is implanted in a patient, the ventricularpacing device may not have knowledge of a short A-V_(ACT) interval. Inthese examples, having the atrial device pacing to maintainV_(ACT)-V_(ACT) timing may help keep the atrial and ventricular devicesin synch.

Maintaining the V_(ACT)-A interval after a shortened A-V_(ACT) intervalmay tend to decrease the length of the interval between atrial events.In other words, maintaining the V_(ACT)-A interval after a shortenedA-V_(ACT) interval may increase the atrial rate of the patient to a ratethat is greater than the baseline atrial pacing rate. In order to bringthe patient's heart rate back to the baseline atrial pacing rate incases where the A-V_(ACT) interval is shortened for a plurality ofcardiac cycles, the processing module may extend the V_(ACT)-A intervalto a value that is greater than T2. In some examples, the processingmodule may maintain the V_(ACT)-A interval at a value of T2 seconds overa plurality of cardiac cycles having shortened A-V_(ACT) intervals untilit becomes apparent that the shortened A-V_(ACT) interval will likelypersist. If the processing module determines that a shortened A-V_(ACT)interval is likely to persist, then the processing module may lengthenthe V_(ACT)-A interval (e.g., to a value of greater than T2) in order tomaintain the baseline atrial pacing interval T3 during subsequentcardiac cycles such that the patient's heart rate is maintained at thebaseline atrial pacing rate. In some examples, the processing module maydetermine that the short A-V_(ACT) interval is persistent if greaterthan a threshold number of cardiac cycles include short A-V_(ACT)intervals. For example, the processing module may determine that theshort A-V_(ACT) interval may persist if greater than a threshold numberof consecutive A-V_(ACT) intervals are short.

In examples where the processing module detects a long A-V_(ACT)interval (e.g., greater than T1), the processing module may maintain thenormal V_(ACT)-A interval timing (e.g., T2) such that theV_(ACT)-V_(ACT) interval will be maintained during the subsequentcardiac cycle, assuming the A-V_(ACT) interval of the subsequent cardiaccycle returns to the normal A-V_(ACT) interval length. In some examples,the A-V_(ACT) interval may return to the normal length in a subsequentcardiac cycle, thereby maintaining the patient's ventricular rate.However, in other examples, the A-V_(ACT) interval may not return tonormal. Instead, the long A-V_(ACT) interval may persist for a pluralityof cardiac cycles.

In some examples, the processing module may maintain the normalV_(ACT)-A interval over a plurality of cardiac cycles having longA-V_(ACT) intervals until it becomes apparent that the long A-V_(ACT)intervals will likely persist. If the processing module determines thata long A-V_(ACT) interval is likely to persist, then the processingmodule may shorten the V_(ACT)-A intervals (e.g., to a value less thanT2) in order to maintain the baseline atrial pacing interval duringsubsequent cardiac cycles. In some examples, the processing module maydetermine that the long A-V_(ACT) intervals will likely persist ifgreater than a threshold number of cardiac cycles include long A-V_(ACT)intervals. For example, the processing module may determine that thelong A-V_(ACT) interval condition may persist if greater than athreshold number of consecutive A-V_(ACT) intervals are long.

In some examples, ventricular activation may go undetected subsequent toan atrial event. The processing module may make the determination thatventricular activation has gone undetected after an atrial event whenthe processing module has not detected ventricular activation (e.g., aFFRW) within a threshold amount of time after an atrial event. Thethreshold amount of time may be an amount of time in which a ventricularactivation should likely have been detected during normal or longA-V_(ACT) intervals. For example, the threshold amount of time may beset to a value that is greater than an expected long A-V_(ACT) interval,e.g., within approximately 400 ms of the atrial event. In examples wherethe processing module determines that ventricular activation has wentundetected, the processing module may schedule the subsequent atrialpace in a manner that maintains the baseline atrial pacing interval. Forexample, the processing module may set the atrial pace to occur T3seconds after the last detected atrial event when the processing moduledetermines that ventricular activation went undetected subsequent to thelast atrial event.

In some examples, the processing module may detect multiple ventricularactivations after an atrial event. In these examples, the processingmodule may adjust atrial pacing timing in order to prevent pacingagainst closed AV valves, which may create patient symptoms. Forexample, upon detection of multiple ventricular activations subsequentto a single atrial event, the processing module may delay atrial pacingsuch that atrial pacing occurs a period of time after the last of thedetected ventricular activations such that the atrium is not paced whilethe AV valves are closed.

The atrial device of the present disclosure may operate as a stand aloneimplantable device. In other words, the atrial device may operate as thesole pacing device implanted in the heart in some examples. Although theatrial device may operate as the sole pacing device implanted within theheart, in other examples, the atrial device may operate along with animplanted leadless ventricular pacing device (hereinafter “ventriculardevice”). The ventricular device of the present disclosure may beimplanted within a ventricle of the heart, sense ventriculardepolarization, and pace the ventricle. The combination of the atrialand ventricular devices may be referred to herein as a leadless pacingsystem (e.g., leadless pacing system 202 of FIG. 11).

In some examples the atrial and ventricular devices may be implantedinto the patient at the same time, e.g., during the same implantprocedure. In other examples, the ventricular device may be implanted ata later time. For example, the patient may initially have the atrialdevice implanted to treat sick sinus syndrome (e.g., bradycardia), thenhave the ventricular device implanted at a later time after the patientdevelops AV block. In still other examples, the atrial device of thepresent disclosure may be implanted some time after the ventriculardevice has already been implanted in an earlier procedure. For example,the atrial device may be implanted after the ventricular device if thepatient develops pacemaker syndrome subsequent to implantation of theventricular pacing device.

The atrial device of the present disclosure may operate reliably withoutmodification when a ventricular device has been added to the patient'sheart to form a leadless pacing system. Put another way, the atrialdevice of the present disclosure may not require modification (e.g.,reprogramming) in order to function along with a subsequently implantedventricular device. The atrial device may operate even when theventricular device is added because the atrial device controls atrialpacing timing based on sensed ventricular activation, independent on theorigin of the sensed ventricular activation. For example, the atrialdevice may control pacing timing in the manner described herein whetherthe ventricular activation detected by the atrial device arises due tointrinsic ventricular depolarization or due to ventricular pacing by theventricular device. Accordingly, the atrial device of the presentdisclosure may function in a variety of different circumstances withoutmodification, e.g., as a stand-alone device or implanted along withanother device.

Although the atrial device of the present disclosure may not requireadditional programming upon implantation of a ventricular device, insome examples, the ventricular device may be programmed to functionalong with the atrial device in order to provide more optimal cardiacpacing. Put another way, in some examples, the ventricular device may beconfigured (e.g., programmed) to operate along with the atrial device inorder to assure that the leadless pacing system performs at an optimallevel. For example, as described herein, the ventricular device may beprogrammed such that the ventricular device paces at a backup rate(e.g., less than the atrial pacing rate) for situations in which atrialdepolarization does not precipitate a ventricular depolarization, e.g.,during AV block. In this example, the ventricular device may pace theventricle when the ventricular device does not detect intrinsicventricular depolarization within a period of time, e.g., due to AVblock in the heart. Operation of the atrial and ventricular devices isdescribed hereinafter with reference to FIGS. 11-12.

Although the processing module may control atrial pacing timing based onwhen ventricular activation occurs relative to the atrial event thatpreceded the ventricular activation, the processing module may controlatrial pacing timing based on other measured intervals in some examples.For example, the processing module may control atrial pacing timingbased on the amount of time between a first ventricular activation eventduring a first cardiac cycle and a second ventricular activation eventduring a second cardiac cycle that occurs subsequent to the firstcardiac cycle. The amount of time between two consecutive V_(ACT)events, i.e., the first and second ventricular activation events, may begenerally referred to herein as a “V_(ACT)-V_(ACT) interval.” In thisexample, the processing module may first determine the amount of timebetween the first and second ventricular activation events and thenschedule an atrial pace based on the amount of time between the firstand second ventricular activation events. Although the processing modulemay control atrial pacing timing based on A-V_(ACT) and V_(ACT)-V_(ACT)intervals, it is contemplated that the processing module mayadditionally or alternatively control atrial pacing timing based onother measured intervals, such as A-A intervals.

The processing module may control atrial pacing timing based on thelength of the V_(ACT)-V_(ACT) interval in a variety of different ways.In examples where the processing module detects FFRWs, the amount oftime between two consecutive ventricular activation events may bereferred to herein as an “FF-FF interval.” In these examples, theprocessing module may control atrial pacing timing based on the value ofthe FF-FF interval. In examples where the processing module detects S1heart sounds, the amount of time between two consecutive ventricularactivation events may be referred to herein as an “S1-S1 interval.” Inthese examples, the processing module may control atrial pacing timingbased on the value of the S1-S1 interval.

The processing module may control atrial pacing timing in different waysdepending on the duration of the V_(ACT)-V_(ACT) interval. TheV_(ACT)-V_(ACT) interval may be characterized as having a normalduration, a short duration, or a long duration. During normal AVconduction in the heart, the V_(ACT)-V_(ACT) interval may becharacterized as having a normal duration. A normal V_(ACT)-V_(ACT)interval may be stored in memory. The normal V_(ACT)-V_(ACT) intervalmay be the expected value of the interval between two consecutiveventricular activation events during normal AV conduction in the heart.The duration of the V_(ACT)-V_(ACT) interval during normal AV conductionmay be referred to herein as a “baseline ventricular interval value.”Normal duration for the V_(ACT)-V_(ACT) interval (i.e., the baselineventricular interval value) when the heart is being paced at 60 bpm maybe approximately 1000 ms. FIG. 4 illustrates atrial pacing timing basedon detected ventricular activations (e.g., FFRWs or S1 heart sounds)during normal AV conduction. In FIG. 4, the V_(ACT)-V_(ACT) (e.g.,FF-FF) interval has a consistent value of T4. During normal AVconduction, when the V_(ACT)-V_(ACT) interval has a normal duration, theprocessing module may schedule the atrial pace to occur T2 seconds afterthe second detected V_(ACT) event.

The timing between consecutive ventricular activation events may deviatefrom the normal V_(ACT)-V_(ACT) interval. In some examples, theV_(ACT)-V_(ACT) interval may be shortened (e.g., the FF-FF interval isless than T4). The V_(ACT)-V_(ACT) interval may be shortened in someexamples due to a PVC. In some examples, the processing module maydetermine that the V_(ACT)-V_(ACT) interval is a short V_(ACT)-V_(ACT)interval when the V_(ACT)-V_(ACT) interval is shorter than the normalV_(ACT)-V_(ACT) interval by a threshold amount of time. In otherexamples, the V_(ACT)-V_(ACT) interval may be lengthened, e.g., due toAV block. The processing module may determine that the V_(ACT)-V_(ACT)interval is a long V_(ACT)-V_(ACT) interval when the detectedV_(ACT)-V_(ACT) interval is longer than a normal V_(ACT)-V_(ACT)interval by a threshold amount of time. Operation of the atrial deviceduring normal V_(ACT)-V_(ACT) intervals, short V_(ACT)-V_(ACT)intervals, and long V_(ACT)-V_(ACT) intervals is described herein.

FIG. 1 shows a leadless atrial pacemaker device 100 (hereinafter “atrialdevice 100”) that may be configured for implantation in a patient 102(FIG. 3). For example, atrial device 100 may be configured forimplantation within right atrium 104 of patient 102. Atrial device 100may be configured to monitor electrical activity of heart 106 and/orprovide electrical therapy to heart 106.

Atrial device 100 includes a housing 108, fixation tines 110-1, 110-2,110-3, 110-4 (collectively “fixation tines 110”), and electrodes 112-1,112-2. Housing 108 may have a pill-shaped cylindrical form factor insome examples. Fixation tines 110 are configured to connect (e.g.,anchor) atrial device 100 to heart 106. Fixation tines 110 may befabricated from a shape memory material, such as Nitinol. In someexamples, fixation tines 110 may connect atrial device 100 to heart 106within one of the chambers of heart 106. For example, as illustrated anddescribed herein with respect to FIG. 3 and FIG. 11, fixation tines 110may be configured to anchor atrial device 100 to heart 106 within rightatrium 104. Although atrial device 100 includes a plurality of fixationtines 110 that are configured to anchor atrial device 100 to cardiactissue in the right atrium, it is contemplated that a leadless deviceaccording to the present disclosure may be fixed to cardiac tissue inother chambers of a patient's heart using other types of fixationmechanisms.

Atrial device 100 may include one or more electrodes 112 for sensingelectrical activity of heart 106 and/or delivering electricalstimulation to heart 106. Atrial device 100 includes two electrodes 112,although more than two electrodes may be included on an atrial device inother examples. Electrode 112-1 may referred to as “tip electrode112-1.” Electrode 112-2 may be referred to as a “ring electrode 112-2.”Fixation tines 110 may anchor atrial device 100 to cardiac tissue suchthat tip electrode 112-1 maintains contact with the cardiac tissue. Ringelectrode 112-2 may be located on housing 108. For example, ringelectrode 112-2 may be a cylindrical electrode that wraps around housing108. Although ring electrode 112-2 is illustrated as a cylindricalelectrode that wraps around housing 108, ring electrode 112-2 mayinclude other geometries. In some examples, housing 108 may be formedfrom a conductive material. In these examples, housing 108 may act as anelectrode of atrial device 100.

Housing 108 houses electronic components of atrial device 100.Electronic components may include any discrete and/or integratedelectronic circuit components that implement analog and/or digitalcircuits capable of producing the functions attributed to atrial device100 described herein. For example, housing 108 may house electroniccomponents that sense electrical activity via electrodes 112 and/ordeliver electrical stimulation via electrodes 112. Additionally, housing108 may also include memory that includes instructions that, whenexecuted by one or more processing circuits housed within housing 108,cause atrial device 100 to perform various functions attributed toatrial device 100 herein. Housing 108 may also house sensors that sensephysiological conditions of patient 102, such as an accelerometer and/ora pressure sensor.

In some examples, housing 108 may house a communication module thatenables leadless device 100 to communicate with other electronicdevices, such as programmer 114 or other external patient monitor. Insome examples, housing 108 may house an antenna for wirelesscommunication. Housing 108 may also include a power source, such as abattery. Electronic components included within housing are described infurther detail hereinafter.

FIG. 2 shows a functional block diagram of an example atrial device 100configured for implantation within atrium 104 (FIG. 3). FIG. 3 shows atherapy system including atrial device 100 and programmer 114 that maybe used to program atrial device 100 and retrieve data from atrialdevice 100. Atrial device 100 includes a processing module 120, memory122, a signal generator module 124, an electrical sensing module 126, acommunication module 128, a sensor 130, and a power source 132. Powersource 132 may include a battery, e.g., a rechargeable ornon-rechargeable battery.

Modules included in atrial device 100 and ventricular device 200 (FIGS.11-12) represent functionality that may be included in atrial device 100and ventricular device 200 of the present disclosure. Modules of thepresent disclosure may include any discrete and/or integrated electroniccircuit components that implement analog and/or digital circuits capableof producing the functions attributed to the modules herein. Forexample, the modules may include analog circuits, e.g., amplificationcircuits, filtering circuits, and/or other signal conditioning circuits.The modules may also include digital circuits, e.g., combinational orsequential logic circuits, memory devices, etc. Memory may include anyvolatile, non-volatile, magnetic, or electrical media, such as a randomaccess memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), Flash memory, or anyother memory device. Furthermore, memory may include instructions that,when executed by one or more processing circuits, cause the modules toperform various functions attributed to the modules herein.

The functions attributed to the modules herein may be embodied as one ormore processors, hardware, firmware, software, or any combinationthereof. Depiction of different features as modules is intended tohighlight different functional aspects, and does not necessarily implythat such modules must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more modulesmay be performed by separate hardware or software components, orintegrated within common or separate hardware or software components.

Processing module 120 may communicate with memory 122. Memory 122 mayinclude computer-readable instructions that, when executed by processingmodule 120, cause processing module 120 to perform the various functionsattributed to processing module 120 herein. Memory 122 may include anyvolatile, non-volatile, magnetic, or electrical media, such as RAM, ROM,NVRAM, EEPROM, Flash memory, or any other digital media. For example,memory 122 may include pacing instructions and values, such as thebaseline atrial pacing rate, the baseline atrial pacing interval and thebaseline AV interval. The pacing instructions and values may be updatedby programmer 114 (FIG. 3). Pacing instructions included in memory 122may cause atrial device 100 to operate as described herein with respectto FIGS. 4-10.

Processing module 120 may communicate with signal generator module 124and electrical sensing module 126. Signal generator module 124 andelectrical sensing module 126 are electrically coupled to electrodes112. Electrical sensing module 126 is configured to monitor signals fromelectrodes 112 in order to monitor electrical activity of heart 106.Signal generator module 124 is configured to deliver electricalstimulation to atrium 104 via electrodes 112.

Processing module 120 may control signal generator module 124 togenerate and deliver electrical stimulation to atrium 104 via electrodes112. Electrical stimulation may include pacing pulses. In some examples,electrical stimulation may also include anti-tachycardia pacing (ATP)therapy. Processing module 120 may control signal generator module 124to deliver electrical stimulation therapy according to one or moreatrial therapy programs including pacing instructions and values, whichmay be stored in memory 122.

Electrical sensing module 126 may include circuits that acquireelectrical signals. Electrical signals acquired by electrical sensingmodule 126 may include intrinsic cardiac electrical activity, such asintrinsic atrial and/or intrinsic ventricular cardiac electricalactivity. Electrical sensing module 126 may filter, amplify, anddigitize the acquired electrical signals to generate raw digital data.Processing module 120 may receive the digitized data generated byelectrical sensing module 126. In some examples, processing module 120may perform various digital signal processing operations on the rawdata, such as digital filtering.

Processing module 120 may sense cardiac events based on the datareceived from electrical sensing module 126. For example, processingmodule 120 may sense atrial events based on the data received fromelectrical sensing module 126. In some examples, processing module 120may sense ventricular activation based on the data received fromelectrical sensing module 126. For example, processing module 120 maydetect FFRWs indicative of ventricular activation based on the datareceived from electrical sensing module 126.

Sensor 130 may comprise at least one of a variety of different sensors.For example, sensor 130 may comprise at least one of a pressure sensorand an accelerometer. Sensor 130 may generate signals that indicate atleast one of an activity level of patient 102, a hemodynamic pressure,and heart sounds. Processing module 120 may detect, for example, anactivity level of patient 102, a hemodynamic pressure, and heart soundsbased on the signals generated by sensor 130.

Communication module 128 may include any suitable hardware (e.g., anantenna), firmware, software, or any combination thereof forcommunicating with another device, such as programmer 114 or a patientmonitor. Under the control of processing module 120, communicationmodule 128 may receive downlink telemetry from and send uplink telemetryto other devices, such as programmer 114 (FIG. 3) or a patient monitor,with the aid of an antenna included in communication module 128. Asdescribed herein, a leadless pacing system (e.g., leadless pacing system202 of FIG. 11) may coordinate pacing of heart 106 based on sensedcardiac electrical and/or mechanical activity without establishment of acommunication link between atrial device 100 and ventricular device 200.Accordingly, communication module 128 is not required to includefunctionality that provides for communication between atrial device 100and ventricular device 200.

Programmer 114 may be a handheld computing device, desktop computingdevice, a networked computing device, etc. Programmer 114 may include acomputer-readable storage medium having instructions that cause aprocessor of programmer 114 to provide the functions attributed toprogrammer 114 in the present disclosure. Atrial device 100 andventricular device 200 may wirelessly communicate with programmer 114.For example, atrial device 100 and ventricular device 200 (FIG. 11) maytransfer data to programmer 114 and may receive data from programmer114. Programmer 114 may also wirelessly program and/or wirelessly chargeatrial device 100 and ventricular device 200.

Data retrieved from atrial device 100 and ventricular device 200 usingprogrammer 114 may include cardiac EGMs stored by atrial device 100 andventricular device 200 that indicate electrical activity of heart 106and marker channel data that indicates the occurrence and timing ofsensing, diagnosis, and therapy events associated with atrial device 100and ventricular device 100. Data transferred to atrial device 100 andventricular device 200 using programmer 114 may include, for example,operational programs for devices 100, 200 that cause devices 100, 200 tooperate as described herein.

Processing module 120 may control atrial pacing timing based on thedetection of ventricular activation events in a variety of differentways. The manner in which processing module 120 controls atrial pacingtiming may depend on when a ventricular activation event occurs relativeto the atrial event that preceded the ventricular activation event. Inother words, the manner in which processing module 120 controls atrialpacing timing may depend on when processing module detects a FFRW or anS1 heart sound relative to the atrial event that preceded the detectedFFRW or the detected S1 heart sound.

FIGS. 4-10 show example ways in which processing module 120 may controlatrial pacing timing based on when ventricular activation is detectedduring the cardiac cycle. FIG. 4 and FIGS. 6-10 include markers (e.g.,lines 134 in FIG. 6) labeled “A.” For purposes of explanation, unlessindicated otherwise, it may be assumed that the label “A” indicates anatrial pace delivered to atrium 104.

FIG. 4 includes markers (e.g., dotted lines 136) labeled V_(ACT). MarkerV_(ACT) indicates when processing module 120 detects a ventricularactivation event. As described herein, processing module 120 may detectventricular activation based on FFRWs and/or S1 heart sounds. FIGS. 6-10include markers (e.g., lines 138 in FIG. 6) labeled “FF.” Marker FFindicates when processing module 120 detects FFRWs.

FIG. 4 and FIG. 6 show atrial pacing timing during normal AV conduction.FIG. 4 illustrates the general concept of controlling atrial pacingbased on the detection of ventricular activation. FIG. 6 shows anexample in which processing module 120 detects ventricular activation bydetecting FFRWs. In the example of FIG. 6, processing module 120controls atrial pacing timing based on when FFRWs are detected duringthe cardiac cycle. Atrial pacing timing based on the detection of FFRWsis also described and illustrated with respect to FIGS. 7-10. Althoughdetection of FFRWs and control of atrial pacing timing based on thedetection of FFRWs is described herein with respect to FIGS. 6-10,processing module 120 may also control atrial pacing timing based on thedetection of S1 heart sounds. In examples where processing module 120controls atrial pacing timing based on S1 heart sounds, the timingdiagrams may be similar to FIGS. 6-10, except the FF labels would bereplaced with S1 heart sound labels indicating when S1 heart sounds weredetected.

FIG. 4 shows atrial pacing timing based on the detection of ventricularactivation during normal AV conduction. The A-V_(ACT) interval duringnormal conduction timing may have a value of T1 seconds. Processingmodule 120 may control atrial pacing timing based on the value of theA-V_(ACT) interval (i.e., T1). As illustrated, processing module 120 mayset the subsequent pacing pulse to occur T2 seconds after ventricularactivation is detected during normal AV conduction.

During normal AV conduction, the A-V_(ACT) interval may be characterizedas having a normal duration. In other words, T1 may represent the normalamount of time between an atrial event and ventricular activation duringnormal AV conduction. Processing module 120 may control stimulationgenerator module 124 to deliver pacing pulses at the baseline atrialpacing rate (e.g., 60 bpm) such that the intervals between atrial eventsare approximately equal to the baseline atrial pacing interval. Asdescribed herein, the baseline atrial pacing rate (i.e., the reciprocalof the baseline atrial pacing interval) may be a value maintained byatrial device 100 based on one or more of a variety of differentfactors, such as the activity level of patient 102. With respect toFIGS. 4-10, the baseline atrial pacing interval may be approximately T3seconds.

In examples where processing module 120 determines that the A-V_(ACT)interval is normal (e.g., approximately equal to T1), processing module120 may schedule the next pace to occur approximately T2 seconds afterthe detected ventricular activation. Processing module 120 may determinethe value of T2 based on the baseline atrial pacing interval and themagnitude of the A-V_(ACT) interval. In examples where processing module120 determines the A-V_(ACT) interval has a normal duration (e.g.,approximately T1), processing module 120 may set the next pacing pulseto occur at a time that maintains the baseline atrial pacing interval.In other words, when processing module 120 determines that the A-V_(ACT)interval is approximately equal to T1, processing module 120 may set thenext pacing pulse to occur approximately T2 seconds after the detectionof ventricular activation. The sum of intervals T1 and T2 may beapproximately T3. In this manner, during normal AV conduction over aplurality of cardiac cycles, processing module 120 may controlstimulation generator module 124 to deliver pacing pulses such that thebaseline atrial pacing rate is maintained over the plurality of cardiaccycles.

Processing module 120 may control atrial pacing timing in different waysdepending on the duration of the A-V_(ACT) interval. Although operationof processing module 120 is described above in examples where A-V_(ACT)has a normal duration T1, A-V_(ACT) may have a short duration (e.g.,less than T1) or a long duration (e.g., greater than T1). Processingmodule 120 may control atrial pacing timing differently based on whichA-V_(ACT) duration is detected.

FIG. 5 is a flowchart that illustrates an example method for controllingatrial pacing timing. It may be assumed that the start of the method ofFIG. 5 occurs just prior to an atrial event (paced or sensed).Initially, an atrial event occurs in block (300). In some examples, theatrial event may be a paced atrial event that is initiated bystimulation generator module 124 under control of processing module 120.In other examples, the atrial event that occurs in block (300) may be anintrinsic atrial event that is detected by processing module 120, e.g.,via sensing module 122. The atrial event of block (300) precedes (e.g.,precipitates) a ventricular activation event. Processing module 120 maydetect the ventricular activation event in block (302). In someexamples, processing module 120 may detect the ventricular activationevent based on the detection of a FFRW in block (302). In some examples,processing module 120 may detect the ventricular activation event basedon the detection of an S1 heart sound in block (302).

Processing module 120 may then determine the length of the A-V_(ACT)interval (304). In examples where processing module 120 detectsventricular activation based on the detection of a FFRW, the interval oftime between the atrial event of block (300) and the FFRW detected inblock (302) may be referred to as the A-FF interval. In examples whereprocessing module 120 detects ventricular activation based on thedetection of an S1 heart sound, the interval of time between the atrialevent of block (300) and the S1 heart sound detected in block (302) maybe referred to as the A-S1 interval.

Processing module 120 may then determine when to deliver (i.e.,schedule) a pacing pulse based on the length of the A-V_(ACT) interval(306). Put another way, processing module 120 may determine theV_(ACT)-A interval based on the length of the A-V_(ACT) interval. Ingeneral, the length of the A-V_(ACT) interval may be characterized asnormal, short, or long. Processing module 120 may determine when todeliver a pacing pulse based on which of the A-V_(ACT) intervals aredetected. As described above, when AV conduction is normal (e.g., theA-V_(ACT) interval is approximately T1), processing module 120 may setthe next pacing pulse to occur T2 seconds after the detected ventricularactivation event such that the interval between atrial events isapproximately equal to the baseline atrial pacing interval T3.

In some examples, the A-V_(ACT) interval may not be approximately equalto T1, but instead, the A-V_(ACT) interval may be shorter than T1 orlonger than T1. In examples where processing module 120 determines thatthe A-V_(ACT) interval is longer than T1 (e.g., by a threshold amount oftime), processing module 120 may identify the A-V_(ACT) interval as along A-V_(ACT) interval. In examples where processing module 120identifies the A-V_(ACT) interval is a long interval, processing module120 may control atrial pacing timing in a manner that is different thanthat described above in the scenario in which the A-V_(ACT) interval isa normal interval. Example control of atrial pacing timing when a longinterval is detected is described herein with reference to FIGS. 8A-8B.

In examples where processing module 120 determines that the A-V_(ACT)interval is shorter than T1 (e.g., by a threshold amount of time),processing module 120 may identify the A-V_(ACT) interval as a shortA-V_(ACT) interval. In examples where processing module 120 identifiesthe A-V_(ACT) interval as a short interval, processing module 120 maycontrol pacing timing in a manner that is different than that describedabove in the scenario in which the A-V_(ACT) interval is a normalinterval. Example control of atrial pacing timing when a short intervalis detected is described herein with reference to FIGS. 7A-7B.

After scheduling the pacing pulse, processing module 120 may controlstimulation generator module 124 to deliver the pacing pulse at thescheduled time (308). In some examples, processing module 120 mayinhibit pacing when an intrinsic atrial event is detected prior to thescheduled pacing time. Although processing module 120 may inhibit pacingwhen an intrinsic atrial event is detected prior to the scheduled pacingtime, such inhibition of pacing is not illustrated in FIG. 4 and FIGS.6-10. Instead, FIG. 4 and FIGS. 6-10 illustrate the delivery of pacingpulses during each cardiac cycle in order to illustrate how atrialpacing timing is scheduled based on when ventricular activation isdetected during a cardiac cycle.

As described above, ventricular activation may refer to electricaldepolarization of the ventricular cardiac tissue and the subsequentmechanical contraction of the ventricular cardiac tissue. In oneexample, processing module 120 may detect ventricular activation bydetecting FFRWs. Put another way, detection of FFRWs is one example ofdetecting ventricular activation. Similarly, processing module 120 maydetect ventricular activation by detecting S1 heart sounds. Atrialdevice 100 is described hereinafter as detecting FFRWs and controllingatrial pacing timing based on the detection of FFRWs. Although FIGS.6-10 describe atrial pacing timing based on the detection of FFRWs, itis contemplated that atrial device 100 may control atrial pacing timingbased on S1 heart sounds in a similar manner. For example, the detectionof S1 heart sounds may generally be substituted for the detection ofFFRWs in FIGS. 6-10.

FIG. 6 shows atrial pacing timing based on the detection of FFRWs whenAV conduction is normal. During normal AV conduction, processing module120 may control pacing timing in a similar manner as described abovewith respect to FIGS. 4-5. For example, during normal AV conduction, theA-FF interval may be approximately T1, and processing module 120 may setthe FF-A interval equal to approximately T2 so that the interval betweenatrial events may be approximately equal to the baseline atrial pacinginterval T3. In some examples, normal AV conduction may persist for aperiod of time. While AV conduction persists, processing module 120 maycontinue to control atrial pacing timing according to FIG. 6.

Although normal A-FF intervals of FIG. 6 may persist for a period oftime, in some examples, the duration of A-FF intervals may deviate fromthe normal A-FF interval T1. In some examples, processing module 120 maydetect a short A-FF interval. In general, a short A-FF interval may bean interval that is shorter than the normal A-FF interval, e.g., by athreshold amount of time. Processing module 120 may identify the A-FFinterval as a short interval when the A-FF interval is less than thenormal A-FF interval by a threshold amount of time.

Processing module 120 may control atrial pacing timing in a variety ofdifferent ways when processing module detects a short A-FF interval. Insome examples, processing module 120 may control atrial pacing timing inorder to maintain a normal FF-FF interval (i.e., a normal V-V interval).Control of atrial pacing timing to maintain a normal FF-FF interval isillustrated in FIG. 7A. In other examples, processing module 120 maycontrol atrial pacing timing to maintain a normal A-A interval (e.g., abaseline atrial pacing interval). Control of atrial pacing timing tomaintain a normal A-A interval is illustrated in FIG. 7B.

Two different responses of processing module 120 in response to adetected short A-FF interval are illustrated in FIGS. 7A-7B. FIG. 7Ashows a scenario in which normal atrial pacing timing is maintaineduntil processing module 120 detects a short A-FF interval at 140. InFIG. 7A, processing module 120 schedules the pacing pulse to occurapproximately T2 seconds after detection of the FFRW in response to adetermination that the A-FF interval is a short A-FF interval. Putanother way, processing module 120 sets the subsequent pacing pulse tooccur such that a normal FF-A interval (i.e., T2) is obtained. Bysetting the pacing pulse to occur approximately T2 seconds after thedetected FFRW, processing module 120 may maintain the normal FF-FFinterval (i.e., V-V interval) assuming that the subsequent A-FF intervalreturns to normal (i.e., T1). In FIG. 7A, the normal A-FF interval T1returns at 142 subsequent to the single cardiac cycle including theshortened A-FF interval. Accordingly, in the example of FIG. 7A, theFF-FF interval 144 returns to normal (i.e., approximately T4) during thecardiac cycle that is subsequent to the cardiac cycle including theshort A-FF interval.

As indicated at 146, pacing according to FIG. 7A causes the A-A intervalto shorten (e.g., to a value less than T3) because the sum of the normalFF-A interval (T2) and the shortened A-FF interval 140 is less than T3.It follows then that pacing according to the strategy of FIG. 7A for anextended period of time (i.e., a plurality of cardiac cycles) may causean increase in the atrial pacing rate to a rate that is greater than thedesired baseline atrial pacing rate. FIG. 7B shows control of atrialpacing timing to maintain the A-A interval at the baseline atrial pacinginterval in the scenario where the shortened A-FF intervals arepersistent for an extended period of time.

FIG. 7B shows a scenario in which normal atrial pacing timing ismaintained until processing module 120 detects a short A-FF interval at148. In FIG. 7B, shortened A-FF intervals are persistent for a pluralityof cardiac cycles after detection of the first short A-FF interval at148. In FIG. 7B, processing module 120 controls atrial pacing timing tomaintain a normal A-A interval having a duration of T3. Processingmodule 120 maintains normal A-A intervals by extending the FF-A intervalto a value that is greater than the normal FF-A interval of T2, asindicated at 150. Put another way, upon detecting a short A-FF interval,processing module 120 may extend the FF-A interval to a value that isgreater than the normal FF-A value in order to maintain the A-A intervalat the normal duration of T3. In order to maintain the A-A interval atthe normal duration of T3, processing module 120 may determine how muchshorter the shortened A-FF interval 148 is than the normal interval T1,then add the difference between the normal and shortened A-FF intervalsto the normal FF-A interval T2.

As described above, in some examples, short A-FF intervals may be atemporary in that only one or a few short A-FF intervals occur. However,in other examples, the short A-FF intervals may persist for a period oftime. In some examples, processing module 120 may be configured tocontrol atrial pacing timing under the initial assumption that theinitial short A-FF interval is temporary. For example, processing module120 may be configured to initially respond to a shortened A-FF intervalby controlling atrial pacing timing in the manner described in FIG. 7A.Processing module 120 may be further configured such that if short A-FFintervals persist, processing module 120 may control atrial pacingtiming to maintain a normal A-A interval, as described with respect toFIG. 7B. In this example, processing module 120 may transition fromcontrolling atrial pacing according to FIG. 7A to controlling atrialpacing according to FIG. 7B upon detection of a threshold number ofshort A-FF intervals. In this manner, processing module 120 mayinitially control pacing to maintain the FF-FF interval, but thencontrol pacing in order to maintain the atrial pacing rate at thebaseline atrial pacing rate when the short A-FF intervals are a longterm condition. Upon detection of a normal A-FF interval T1, processingmodule 120 may return to pacing according to FIG. 6.

Referring now to FIGS. 8A-8B, in some examples, processing module 120may detect a long A-FF interval. In general, a long A-FF interval may bean interval that is longer than the normal A-FF interval, e.g., by athreshold amount of time. Processing module 120 may identify the A-FFinterval is a long A-FF interval when the A-FF interval is greater thanthe normal A-FF interval by a threshold amount of time.

Processing module 120 may control atrial pacing timing in a variety ofdifferent ways when processing module 120 detects a long A-FF interval.In some examples, processing module 120 may control atrial pacing timingin order to maintain a normal FF-FF interval (i.e., a normal V-Vinterval). Control of atrial pacing timing to maintain a normal FF-FFinterval after a long A-FF interval is detected is illustrated in FIG.8A. In other examples, processing module 120 may control atrial pacingtiming to maintain a normal A-A interval. Control of atrial pacingtiming to maintain a normal A-A interval after detection of a long A-FFinterval is illustrated in FIG. 8B.

Two different responses of processing module 120 in response todetection of a long A-FF interval are illustrated in FIGS. 8A-8B. FIG.8A shows a scenario in which normal atrial pacing timing is maintaineduntil processing module 120 detects a long A-FF interval at 152. In FIG.8A, processing module 120 schedules the pacing pulse to occurapproximately T2 seconds after detection of the FFRW in response to adetermination that the A-FF interval is a long A-FF interval at 152. Putanother way, processing module 120 sets the subsequent pacing pulse tooccur such that a normal FF-A interval (i.e., T2) is obtained. Bysetting the pacing pulse to occur approximately T2 seconds after thedetected FFRW, processing module 120 may maintain the normal FF-FFinterval in the next cardiac cycle assuming that the subsequent A-FFinterval returns to normal (i.e., T1). In FIG. 8A, the normal A-FFinterval T1 returns at 154 subsequent to the single cardiac cycleincluding the long A-FF interval. Accordingly, as illustrated at 156 inthe example of FIG. 8A, the FF-FF interval returns to normal (i.e.,approximately T4) during the cardiac cycle that is subsequent to thecardiac cycle including the long A-FF interval.

As illustrated at 158, pacing according to FIG. 8A causes the A-Ainterval to lengthen (e.g., to a value greater than T3) because the sumof the lengthened FF-A interval and the normal FF-A interval (T2) isgreater than T3. It follows then that pacing according to the strategyof FIG. 8A may cause a decrease in the atrial pacing rate, at least fora single cardiac cycle. FIG. 8B shows control of atrial pacing timing tomaintain the A-A interval at the baseline atrial pacing interval in thescenario where long A-FF intervals are persistent for an extended periodof time.

FIG. 8B shows a scenario in which normal atrial pacing timing ismaintained until processing module 120 detects a long A-FF interval at160. In FIG. 8B, long A-FF intervals are persistent for a plurality ofcardiac cycles after detection of the first long A-FF interval at 160.In FIG. 8B, processing module 120 controls atrial pacing timing tomaintain a normal A-A interval having a duration of T3. Processingmodule 120 maintains normal A-A intervals by shortening the FF-Ainterval to a value that is less than the normal FF-A interval of T2, asillustrated at 162. Put another way, upon detecting a long A-FFinterval, processing module 120 may shorten the FF-A interval to a valuethat is less than the normal FF-A value in order to maintain the A-Ainterval at the normal duration of T3. In order to maintain the A-Ainterval at the normal duration of T3, processing module 120 maydetermine how much longer the long A-FF interval 162 is than the normalinterval T1, then subtract the difference between the normal and longA-FF intervals from the normal FF-A interval T2.

As described above, in some examples, long A-FF intervals may betemporary such that only one or a few consecutive long A-FF intervalsoccur. However, in other examples, the long A-FF intervals may persistfor a period of time. In some examples, processing module 120 may beconfigured to control atrial pacing timing under the initial assumptionthat the initial long A-FF interval is temporary. For example,processing module 120 may be configured to initially respond to a longA-FF interval by controlling atrial pacing timing in the mannerdescribed in FIG. 8A. Processing module 120 may be further configuredsuch that if long A-FF intervals persist, processing module 120 maycontrol atrial pacing timing to maintain a normal A-A interval, asdescribed with respect to FIG. 8B. In this example, processing module120 may transition from controlling atrial pacing according to FIG. 8Ato controlling atrial pacing according to FIG. 8B upon detection of athreshold number of long A-FF intervals. In this manner, processingmodule 120 may initially control pacing to maintain the FF-FF interval,but then control pacing in order to maintain the atrial pacing rate ator near the baseline atrial pacing rate when the long A-FF intervals area long term condition. Upon detection of a normal A-FF interval (i.e.,T1) after detection of one or more long A-FF intervals, processingmodule 120 may return to pacing according to FIG. 6.

Processing module 120 may control atrial pacing timing according toFIGS. 8A-8B subject to some constraints. For example, processing module120 may be configured to maintain the A-A pacing interval at a valuethat is less than a maximum A-A interval (i.e., a minimum atrial pacingrate). Accordingly, in some examples, processing module 120 may beconfigured to set a pacing pulse such that the A-A interval is less thana maximum A-A interval. The minimum atrial pacing rate (maximum A-Ainterval) may be stored in memory 122 in some examples.

FIG. 9 shows example atrial pacing timing in the case that a FFRW goesundetected by processing module 120 or did not occur due to AV block, asillustrated at 164. Processing module 120 may be configured to pace atthe baseline atrial pacing rate when a FFRW is not detected after anatrial event. Processing module 120 may determine whether a FFRW isabsent after an atrial event based on the amount of time that has passedsince the atrial event. For example, if a threshold amount of time haspassed after an atrial event without detection of a FFRW, processingmodule 120 may determine that a FFRW went undetected during the cardiaccycle. Accordingly, if processing module 120 does not detect a FFRWevent within a threshold amount of time (e.g., within 400 ms),processing module 120 may schedule a pacing pulse to occur T3 secondsafter the last detected atrial event.

FIG. 10 shows example atrial pacing timing in the case that processingmodule 120 detects multiple FFRWs after an atrial event. In thisexample, processing module 120 may detect a first FFRW 166-1 andschedule atrial pacing timing based on the first detected FFRW 166-1.For example, processing module 120 may schedule a pacing pulse to occurbased on the length of the A-FF interval at 168. In some examples,processing module 120 may set the pacing pulse based on whether A-FFinterval is normal, short, or long, as described above with respect toFIGS. 7A-8B. The pacing pulse scheduled based on the A-FF interval at168 is illustrated by the dotted line 170. In cases where processingmodule 120 schedules a pacing pulse based on a first detected FFRW butdetects a second FFRW 166-2 prior to delivery of the scheduled pacingpulse, processing module 120 may determine that multiple FFRWs aredetected.

Upon detecting multiple FFRWs, processing module 120 may control pacingtiming to prevent pacing such that the atrial contraction occurs againsta closed AV valve. For example, upon detection of multiple FFRWssubsequent to a single atrial event, processing module 120 may delayatrial pacing for a period of time to prevent pacing the atrium againsta closed valve. In some examples, processing module 120 may delay atrialpacing for T2 seconds after the last detected FFRW. In examples wherepacing T2 seconds after the last detected FFRW would cause the atrialpacing rate to drop below a minimum atrial pacing rate, processingmodule 120 may pace the atrium such that the minimum atrial pacing rateis not violated.

With respect to FIG. 10, processing module 120 may detect a first FFRWat 166-1. In the example of FIG. 10, the A-FF interval is approximatelyequal to T1. Accordingly, as described above, processing module 120 mayset an initial pacing pulse to occur approximately T2 seconds afterfirst FFRW 166-1. The initial scheduled pacing pulse is illustrated asdotted line 170. Prior to delivering the initially scheduled pacingpulse 170, processing module 120 detects a second FFRW 166-2. Upondetection of the second FFRW 166-2, processing module 120 may update thetime at which the pacing pulse is to be delivered. For example,processing module 120 may update the pacing pulse to occur a period oftime after the second FFRW 166-2 that will likely prevent pacing theatrium while the valve is closed.

FIG. 11 shows an example leadless pacing system 202. Leadless pacingsystem 202 includes atrial device 100 and a leadless ventricularpacemaker device 200 (hereinafter “ventricular device 200”). Ventriculardevice 200 may be configured to pace the ventricle, sense intrinsicventricular depolarizations, and inhibit ventricular pacing in responseto detected ventricular depolarization. The structure of ventriculardevice 200 may be similar to the structure of atrial device 100. Forexample, ventricular device 200 may have a housing, fixation tines, andelectrodes that are similar to housing 108, fixation tines 110, andelectrodes 112 of atrial device 100 (FIG. 1).

The fixation tines of ventricular device 200 are configured to connect(e.g., anchor) ventricular device 200 to heart 106. For example, thefixation tines of ventricular device 200 may be configured to anchorventricular device 200 within the right or left ventricle. Asillustrated and described herein with respect to FIG. 11, ventriculardevice 200 may be implanted within right ventricle 206.

Ventricular device 200 may include two or more electrodes (e.g.,electrodes 222-1, 222-2 of FIG. 12) for sensing electrical activity ofheart 106 and/or delivering electrical stimulation to heart 106.Ventricular device 200 may include a tip electrode and a ring electrode,similar to tip electrode 112-1 and ring electrode 112-2 of atrial device100 (FIG. 1). The fixation tines of ventricular device 200 may anchorventricular device 200 to cardiac tissue such that the tip electrode ofventricular device 200 maintains contact with the cardiac tissue.

Ventricular device 200 may include a housing that is similar to housing108 of atrial device 100. The housing of ventricular device 200 houseselectronic components of ventricular device 200. Electronic componentsmay include any discrete and/or integrated electronic circuit componentsthat implement analog and/or digital circuits capable of producing thefunctions attributed to ventricular device 200 described herein. Forexample, the housing of ventricular device may house electroniccomponents that sense electrical activity via the electrodes ofventricular device 200 and/or deliver electrical stimulation via theelectrodes of ventricular device 200. The housing of ventricular devicemay also include memory that includes instructions that, when executedby one or more processing circuits housed within the housing ofventricular device 200, cause ventricular device 200 to perform variousfunctions attributed to ventricular device 200 herein. Ventriculardevice 200 may also include sensors that sense physiological conditionsof patient 102, such as an accelerometer and/or a pressure sensor.

In some examples, ventricular device 200 may include a communicationmodule that enables ventricular device 200 to communicate with otherelectronic devices, such as programmer 114. In some examples,ventricular device 200 may include an antenna for wireless communicationwith other devices. Ventricular device 200 may also include a powersource, such as a battery.

FIG. 12 shows a functional block diagram of an example ventriculardevice 200 configured for implantation within ventricle 206. Ventriculardevice 200 includes a processing module 208, memory 210, a signalgenerator module 212, an electrical sensing module 214, a communicationmodule 216, a sensor 218, and a power source 220. Power source 220 mayinclude a battery, e.g., a rechargeable or non-rechargeable battery.

Processing module 208 may communicate with memory 210. Memory 210 mayinclude computer-readable instructions that, when executed by processingmodule 208, cause processing module 208 to perform the various functionsattributed to processing module 208 herein. Memory 210 may include anyvolatile, non-volatile, magnetic, or electrical media, such as RAM, ROM,NVRAM, EEPROM, Flash memory, or any other digital media. For example,memory 210 may include ventricular pacing instructions and values, suchas a ventricular pacing rate, which may be updated by programmer 114.Ventricular pacing instructions included in memory 114 may causeventricular device 200 to operate as described herein.

Processing module 208 may communicate with signal generator module 212and electrical sensing module 214. Signal generator module 212 andelectrical sensing module 214 are electrically coupled to electrodes222-1, 222-2 (collectively “electrodes 222”). Electrical sensing module214 is configured to monitor signals from electrodes 222 in order tomonitor electrical activity of heart 106. Signal generator module 212 isconfigured to deliver electrical stimulation to heart 106 via electrodes222. Processing module 208 may control signal generator module 212 togenerate and deliver electrical stimulation to ventricle 206 viaelectrodes 222. Electrical stimulation may include pacing pulses.Processing module 208 may control signal generator module 136 to deliverelectrical stimulation therapy according to one or more ventriculartherapy programs that define a ventricular pacing rate. The ventriculartherapy programs may be stored in memory 210.

Electrical sensing module 214 may include circuits that acquireelectrical signals. Electrical signals acquired by electrical sensingmodule 214 may include intrinsic cardiac electrical activity, such asintrinsic ventricular depolarizations. Electrical sensing module 214 mayfilter, amplify, and digitize the acquired electrical signals togenerate raw digital data. Processing module 208 may receive thedigitized data generated by electrical sensing module 214. In someexamples, processing module 208 may perform various digital signalprocessing operations on the raw data, such as digital filtering.Processing module 208 may sense ventricular events (e.g., intrinsicventricular depolarizations) based on the data received from electricalsensing module 214.

Sensor 218 may comprise at least one of a variety of different sensors.For example, sensor 218 may comprise at least one of a pressure sensorand an accelerometer. Sensor 218 may generate signals that indicate anactivity level of patient 102. Processing module 208 may detect anactivity level of patient 102 based on the signals generated by sensor218.

Communication module 216 may include any suitable hardware (e.g., anantenna), firmware, software, or any combination thereof forcommunicating with another device, such as programmer 114 or a patientmonitor. Under the control of processing module 208, communicationmodule 216 may receive downlink telemetry from and send uplink telemetryto other devices, such as programmer 114 or a patient monitor, with theaid of an antenna included in communication module 216. As describedherein, a leadless pacing system (e.g., leadless pacing system 202 ofFIG. 11) may coordinate pacing of heart 106 based on sensed cardiacelectrical and/or mechanical activity without establishment of acommunication link between atrial device 100 and ventricular device 200.Accordingly, communication module 216 is not required to includefunctionality that provides for communication between atrial device 100and ventricular device 200.

Ventricular device 200 may wirelessly communicate with programmer 114.For example, ventricular device 200 may transfer data to programmer 114and may receive data from programmer 114. Programmer 114 may alsowirelessly program ventricular device 200. For example, programmer 114may wirelessly program operational parameters of ventricular device 200,such as the ventricular pacing rate.

In general, ventricular device 200 may be configured to pace ventricle206 at a ventricular pacing rate. In the case where ventricular device200 detects an intrinsic ventricular depolarization prior to deliveringthe pacing stimulus according to the ventricular pacing rate,ventricular device 200 may withhold stimulation. The ventricular pacingrate may be set such that ventricular device 200 tends to pace ventricle206 in situations in which AV conduction is blocked. In other words, theventricular pacing rate may be set at a rate that provides backup pacingto ensure that ventricle 206 is paced in situations where intrinsicventricular depolarizations do not arise as a result of atrialdepolarizations. In some examples, the ventricular pacing rate may be arate that is less than or equal to the atrial pacing rate. For example,the ventricular pacing rate may be set to 10-20 paces per minute lessthan the atrial rate (e.g., approximately 40 ppm). The ventricularpacing rate may also be expressed as a ventricular pacing interval. Theventricular pacing interval may be the reciprocal value of theventricular pacing rate. Operation of ventricular device 200 withrespect to FIG. 12 is now described.

Memory 210 may store the ventricular pacing rate and/or the ventricularpacing interval. In some examples, the ventricular pacing rate mayinitially be programmed into memory 210 upon initial implantation ofventricular device 200. The ventricular pacing rate may be updated insome examples. For example, a clinician may use programmer 114 to updatethe ventricular pacing rate. In some examples, processing module 208 mayautomatically update the ventricular pacing rate. For example,processing module 208 may determine an activity level of patient 102 andmodify the ventricular pacing rate based on the activity level ofpatient 102. In this example, processing module 208 may increase theventricular pacing rate upon determining that the patient activity levelhas increased. Processing module 208 may decrease the ventricular pacingrate upon determining that the patient activity level has decreased.

Processing module 208 may control signal generator module 212 to deliverpacing pulses at the ventricular pacing rate stored in memory 210.Processing module 208 may also inhibit the delivery of pacing pulses toventricle 206 when processing module 208 detects an intrinsicventricular depolarization. Accordingly, after a paced or sensedventricular event, processing module 208 may schedule the nextventricular pacing pulse to occur such that the amount of time betweenthe scheduled pacing pulse and the previous ventricular event is equalto the ventricular pacing interval.

As described above, the ventricular pacing rate may be set to a valuethat is less than the atrial pacing rate. In examples where theventricular pacing rate is less than the atrial pacing rate and normalAV conduction is present in heart 106, ventricular device 200 maytypically not pace ventricle 200. Instead, the pacing pulses deliveredby atrial device 100 may cause intrinsic ventricular depolarizationsthat in turn cause ventricular device 200 to inhibit a scheduledventricular pacing pulse. Accordingly, in the absence of AV block inheart 106, ventricular activation (e.g., FFRWs and S1 heart sounds)detected by atrial device 100 may typically arise due to intrinsicventricular depolarizations.

Ventricular device 200 may pace ventricle 206 when AV block is presentin heart 106. In some examples, AV block may be present temporarily inheart 106, e.g., for one or a few cardiac cycles. In other examples, AVblock may persist for longer periods of time, or may be permanent. Inexamples where AV block occurs, the ventricular activation events (e.g.,FFRWs and S1 heart sounds) detected by atrial device 100 may arise frompaced ventricular events. In examples where AV block occurs temporarilybetween periods of AV conduction, the ventricular activations detectedby atrial device 100 may arise from paced ventricular events duringperiods of AV block and may arise due to intrinsic ventriculardepolarizations during periods of AV conduction. Accordingly, in onesense, the ventricular pacing rate of ventricular device 200 may bethought of as a backup pacing rate that causes ventricular device 200 topace in circumstances where AV block occurs.

FIG. 8A may illustrate an example of how ventricular device 200 mayprovide backup ventricular pacing during AV block. With respect to FIG.8A, if it is assumed that AV block is present during the atrial event at224, it may be assumed that the FF event (226) detected by atrial device100 arose due to a paced ventricular event instead of an intrinsicventricular depolarization. In this case, the long A-FF interval at 152would be due to the lower ventricular pacing rate (i.e., lower than theatrial pacing rate) implemented by ventricular device 200. As describedabove, ventricular device 200 would provide a pacing pulse to theventricle at the expiration of the ventricular pacing interval sinceventricular device 200 would not have been inhibited from pacing by adetected intrinsic ventricular depolarization.

Although processing module 120 may control atrial pacing timing based onthe length of the A-V_(ACT) interval (e.g., the A-FF interval),processing module 120 may also control atrial pacing timing based onother measured intervals in some examples. For example, processingmodule 120 may control atrial pacing timing based on the amount of timebetween two consecutive V_(ACT) events (e.g., two consecutive FFevents). In this example, processing module 120 may first determine thelength of the V_(ACT)-V_(ACT) interval (e.g., FF-FF interval), and thenschedule an atrial pace based on the length of the V_(ACT)-V_(ACT)interval. Although processing module 120 may control atrial pacingtiming based on A-V_(ACT) and V_(ACT)-V_(ACT) intervals, it iscontemplated that processing module 120 may additionally oralternatively control atrial pacing timing based on other measuredintervals, such as A-A intervals. Control of atrial pacing timing basedon the duration of the V_(ACT)-V_(ACT) interval is described hereinafterassuming that processing module 120 detects FFRWs.

Processing module 120 may control atrial pacing timing in different waysdepending on the duration of the FF-FF interval. In some examples,processing module 120 may detect a short FF-FF interval. In general, ashort FF-FF interval may be an interval that is shorter than the normalFF-FF interval, e.g., by a threshold amount of time. Processing module120 may identify the FF-FF interval as a short interval when processingmodule 120 determines that the FF-FF interval is less than the normalFF-FF interval by a threshold amount of time.

Processing module 120 may control atrial pacing timing in a variety ofdifferent ways when processing module 120 detects a short FF-FFinterval. In some examples where processing module 120 detects a shortFF-FF interval, processing module 120 may maintain the normal FF-Ainterval timing (e.g., T2) such that the normal FF-FF interval will bemaintained during the subsequent cardiac cycle, assuming the A-FFinterval of the subsequent cycle returns to the normal duration of T1.FIG. 7A shows an example in which processing module 120 may detect ashortened FF-FF interval and maintains the FF-A interval such that thesubsequent FF-FF interval is maintained at the normal duration. In otherexamples, with respect to FIG. 7B, processing module 120 may lengthenthe FF-A interval (e.g., to a value of greater than T2) in order tomaintain the baseline atrial pacing interval T3 during subsequentcardiac cycles such that the patient's heart rate is maintained at thebaseline atrial pacing rate.

In some examples, processing module 120 may detect a long FF-FFinterval. In general, a long FF-FF interval may be an interval that islonger than the normal FF-FF interval, e.g., by a threshold amount oftime. Processing module 120 may identify the FF-FF interval as a longFF-FF interval when processing module 120 determines that the FF-FFinterval is greater than the normal FF-FF interval by a threshold amountof time.

With respect to FIGS. 8A-8B, processing module 120 may control atrialpacing timing in a variety of different ways when processing module 120detects a long FF-FF interval. In some examples where processing module120 detects a long FF-FF interval (e.g., greater than T4), processingmodule 120 may maintain the normal FF-A interval timing (e.g., T2) suchthat the FF-FF interval will be maintained at the normal duration duringthe subsequent cardiac cycle, assuming the A-FF interval of thesubsequent cardiac cycle returns to the normal A-FF interval length.FIG. 8A shows an example in which processing module 120 may detect along FF-FF interval and maintain the FF-A interval such that thesubsequent FF-FF interval is maintained at the normal duration. In someexamples, as illustrated in FIG. 8B, processing module 120 may shortenthe FF-A intervals (e.g., to a value less than T2) in order to maintainthe baseline atrial pacing interval during subsequent cardiac cycles.

Various examples have been described. One example is a method comprisingdetecting a ventricular activation event using an atrial pacing deviceconfigured for implantation within an atrium, determining a length of aninterval between the ventricular activation event and a previous atrialevent that preceded the ventricular activation event, scheduling a timeat which to deliver a pacing pulse to the atrium based on the length ofthe interval, and delivering the pacing pulse at the scheduled time. Insome examples, the ventricular electrical activity is a far-field R-wave(FFRW). In some examples, detecting the ventricular activation eventcomprises detecting a FFRW, wherein determining the length of theinterval between the ventricular activation event and the previousatrial event comprises determining a length of an interval between thedetected FFRW and the previous atrial event, and wherein scheduling thetime at which to deliver the pacing pulse to the atrium comprisesscheduling a time at which to deliver a pacing pulse based on the lengthof the interval between the detected FFRW and the previous atrial event.

In some examples, the method further comprises generating signals thatindicate mechanical cardiac characteristics, and detecting contractionof a ventricle based on the generated signals. The mechanical cardiaccharacteristics may include heart sounds. In some examples, detectingthe ventricular activation event comprises detecting an S1 heart sound,wherein determining the length of the interval between the ventricularactivation event and the previous atrial event comprises determining alength of an interval between the detected S1 heart sound and theprevious atrial event, and wherein scheduling the time at which todeliver the pacing pulse to the atrium comprises scheduling a time atwhich to deliver the pacing pulse based on the length of the intervalbetween the detected S1 heart sound and the previous atrial event.

In some examples, the method further comprises storing a baselineatrioventricular (AV) value that is an expected value of the intervalbetween the ventricular activation event and the previous atrial eventduring normal AV conduction of the heart. In some examples, the methodfurther comprises comparing the determined length of the interval to thebaseline AV value, and scheduling the time at which to deliver thepacing pulse to the atrium based on the comparison. In some examples,the method further comprises identifying the interval as having one of anormal duration, a short duration, or a long duration based on thecomparison, and scheduling the time at which to deliver the pacing pulseto the atrium based on whether the interval is identified as having anormal duration, a short duration, or a long duration. In some examples,the method further comprises comparing the determined length of theinterval to the baseline AV value, identifying the interval as having anormal duration when the determined length of the interval isapproximately equal to the baseline AV value, identifying the intervalas having a short duration when the determined length of the interval isless than the baseline AV value by a threshold amount, and schedulingthe time at which to deliver the pacing pulse to the atrium based onwhether the interval is identified as having the normal duration or theshort duration. In some examples, the method further comprises comparingthe determined length of the interval to the baseline AV value,identifying the interval as having a normal duration when the determinedlength of the interval is approximately equal to the baseline AV value,identifying the interval as having a long duration when the determinedlength of the interval is greater than the baseline AV value by athreshold amount, and scheduling the time at which to deliver the pacingpulse to the atrium based on whether the interval is identified ashaving the normal duration or the long duration.

In some examples, the method further comprises determining that theventricular activation event went undetected, and scheduling a pacingpulse based on the determination that the ventricular activation eventwent undetected.

In some examples, the method further comprises determining when multipleventricular activation events have occurred after the previous atrialevent but before the scheduled time at which the pacing pulse is to bedelivered, and scheduling a new time at which to deliver a pacing pulseto the atrium based on the determination that multiple ventricularactivation events have occurred.

These and other examples are within the scope of the following claims.

What is claimed is:
 1. A device comprising: a signal generator moduleconfigured to deliver pacing pulses to an atrium via one or moreelectrodes; a processing module configured to: detect a firstventricular activation event; detect a second ventricular activationevent subsequent to the first ventricular activation event; determine alength of a single interval between the first and second ventricularactivation events; compare the length of the single interval to abaseline ventricular interval value; schedule a time at which to delivera pacing pulse to the atrium based on the comparison of the length ofthe single interval to the baseline ventricular interval value; andcontrol the signal generator module to deliver the pacing pulse at thescheduled time; and a housing configured for implantation within theatrium, wherein the housing encloses the signal generator module and theprocessing module.
 2. The device of claim 1, further comprising a memorythat stores the baseline ventricular interval value, the baselineventricular interval value being an expected value of the singleinterval between the first and second ventricular activation eventsduring normal AV conduction of the heart.
 3. The device of claim 1,wherein the processing module is configured to: identify the singleinterval as having one of a normal duration, a short duration, or a longduration based on the comparison; and schedule the time at which todeliver the pacing pulse to the atrium based on whether the singleinterval is identified as having a normal duration, a short duration, ora long duration.
 4. The device of claim 1, wherein the length of thesingle interval is a first length of a first single interval, the timeis a first time, and the pacing pulse is a first pacing pulse, andwherein the processing module is further configured to: detect a thirdventricular activation event subsequent to the second ventricularactivation event; determine a second length of a second single intervalbetween the second and third ventricular activation events; compare thesecond length of the second single interval to the baseline ventricularinterval value; schedule a second time at which to deliver a secondpacing pulse to the atrium based on the comparison of the second lengthof the second single interval to the baseline ventricular intervalvalue; and control the signal generator module to deliver the secondpacing pulse at the scheduled second time.
 5. The device of claim 4,wherein the first time at which the first pacing pulse is deliveredoccurs between the second and third ventricular activation events.